The invention relates to a process for the operation of a roller with a roller shell which is rotatable on a support fixed against rotation and is braced on this support by at least one bracing element, and having at least one device for affecting the temperature of the roller shell, whereby at least one apparatus for controlling the temperature of the interior of the roller shell, and at least one apparatus for controlling the temperature of the outer surface of the roller shell are respectively provided.
Rollers of this type are known from PCT Application No. WO 85/01532 or German Patent No. 3,429,695 and are preferably used for the treatment of the surfaces of continuous materials under simultaneous pressure and temperature action, in particular fibrous materials, for example, paper, cardboard, non-wovens, textiles or plastics. A particularly suitable use is the smoothing of paper webs in glazing rollers or calenders, where the paper fibers are more easily deformable because of the raised temperature and where a smoothing and glazing effect on the surface of the paper can be attained under the effects of pressure.
It is disadvantageous in these known rollers that in many cases the heating time required for heating the roller to the required operational temperature at startup of the glazing rollers or calender is too long and sometimes requires several hours. Furthermore, irregularities appear in the startup or heating phases which may lead to bursting of the roller shell and could not be overcome up to now.
It is furthermore disadvantageous that the treatment temperature on the exterior surface of the roller attainable with these rollers is limited, because the components required in the interior of the roller and the heating oil are only usable up to a set temperature limit. Furthermore, energy losses in rollers of this type are considerable.
Instead of heating the roller from inside, it was proposed in PCT Application No. WO-85/01532, for example, to provide an exterior heater acting on the outer surface. In this connection irregularities also occur which may lead to the destruction of the roller shell during heating. Here, rollers with hard rubber shells, which are customarily used in glazing rollers and calenders and where the outer skin already is in a certain stress state, have proven to be particularly sensitive. Because exterior heating is applied as a rule shortly ahead of the press gap, temperature variations occur across the periphery of the roller shell during heating at low rpm as well as during operation with higher rpm, which lead to disadvantageous stress because of temperature changes and also result in considerable energy losses.
Deflection compensation rollers, where the rotating roller shell is braced on the support by at least one bracing element, for example with at least one pressure chamber or a plurality of hydraulic or other bracing elements, have proven to be particularly suitable for attaining even pressure, or pressure acting in accordance with a desired profile, and even heat transfer, or heat transfer acting in accordance with a desired profile, from the surface of the roller to the continuous material.
This is of particular advantage with large roller widths up into the range of 10 m, as are customary with paper machines.
Various heatable deflection compensation rollers of the previously mentioned type are known, for example, from U.S. Pat. No. 4,282,638. Lateral nozzles are provided on the support here, from which a hot temperature-transfer medium is sprayed on the interior of the roller shell and the roller shell is heated by means of impact flow heating.
On the other hand, deflection compensation rollers with a plurality of hydrostatic support elements are known from Swiss Patent No. 577,598 or U.S. Pat. No. 4,282,639, the support surfaces of which have bearing pockets, which are supplied with a heated hydraulic medium via a pressure chamber with bores in the support. The interior of the roller shell is heated here to a set temperature by the hot hydraulic medium.
Analogous disadvantages occur when the glazing rollers are stopped and the rollers must be cooled, for example for replacement or finishing work. Considerable time is required for this, too, and there is the danger of damaging or destroying the roller shell when using a cooling agent from the interior or the exterior.